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Moulding and Casting

Assignment 12

For week 12 we were asked to explore molding and casting using a 2 step mold. Our first task was to model an object and machine it using a 3D milling process. I decided to make a mold of one of the many widgets I have my students model in my classes. I started by using Inventor to make the initial .ipt file.

Mould Inventor File

Once I was satisfied with the model of my widget I uploaded the file to Autodesk Fusion 360. I am starting to really find this program to quite useful for generating g-code for both our CNC router and our Tormach PNC 440 mill. Below are the toolpaths that were generated. I chose to use the 1/4 inch end mill as I was hoping that it would do a good job of smoothing out the radius on both the x and y axis. I even took some time to tweak some of the step over and finish pass parameters.

After finishing the toolpaths and moving it to the CNC router I proceeded to mill a part. We have a local business whol donates large amount of REN shape/wood cut offs to us as he cannot use them for his large parts. I really like this material as it is very easy to machine. Can take a pretty agressive feed/speed and leaves a really smooth/clean finish for our parts. So far I have used the gray, blue and tan versions of this material. My part took a little under an hour to finish milling.

After the milling process was completed I proceeded to put sides around my milled part and used Oomoo to create a fleible silicone mold to be used for casting. The mixing of the Oomoo was really simple as we ordered two sample kits and simply mixed part A and part B together. After mixing I carefully poured the Oomoo into the mold to avoid any air bubbles. One thing I noticed was that the table that I was working on was not completely level so my mold is not 100% true.

The directions for the Oomoo state that the product should be left to cure for 24 hours. After leaving it over night and most the next day I decided to attempt to de-mold my Oomoo. At first I was a little hesitant as I didn't want to ruin anything but the silicone spray that we used as a mold release did it's job perfectly. The resulting soft/flexible mold seems to be really smooth although more dense than what I was expecting

The last step in the process was to mix up our dry stone material pour the it into the mold and let it set. After the set-up was complete we would have a casting of our original part. This went really smoothly and the part came out pretty decent. I think the only issues that I still need to sort out would be to either use a smaller diameter endmill to reduce the amount of stepping or to look into using a bull nose end mill to help smooth out the round.